1. Field of the Invention
The present invention relates generally to bar codes, and particularly to bar codes employed in mail processing.
2. Technical Background
In mail processing systems there are many situations in which it is useful to be able to mark mail pieces with machine-readable symbols. These “marks” may represent postal codes, positioning indicators, postage indications, mail bundle types, and many other attributes.
One approach to marking mail pieces, bundles, or other types of mail items includes the use of a symbology known as the Facing Identification Mark (FIM). This mark is simple and conveys no information other than its existence. Referring to FIGS. 1A–1D, diagrams of USPS FIMS are shown. The United States Postal Service uses a set of FIMs for Facing as well as special sortation indicators. They are not particularly suitable for omni direction reading. An interesting point which illustrates the problems about “extending” FIMs is that A, B, and C were designed at the same time, whereas FIM D was added later. Note that if the space and bar sizes are treated loosely enough, which is often the case in order to get good read rates, the reader may confuse certain marks. For example, there is a FIM A within the FIM D (ignore leftmost and rightmost bars).
Referring to FIGS. 2A–2F, UKRM FIM symbol diagrams are shown. The United Kingdom Royal Mail also uses a set of FIMs for facing as well as mail class information. The two examples shown below include a gray scale imaging version, a binarized imaging version that preserves large black areas, and an edge binarized image that does not preserve large black areas. Gray scale imaging produces a good image, but it is more complex and costly. The edge binarization design definitely has issues with wide bars being hollowed out by the imaging system. In order to mitigate this problem, a robust reader is required. Unfortunately, a robust reader is typically more costly, involves increased complexity, and increased reader execution time. FIMs are also not suitable for omni directional reading, but since they are typically used on letters only, this is usually not a problem. It is noted that USPS FIMs do not have hollowing issues because the bar width is uniform and relatively small.
On the other hand, the FIM approach has other drawbacks. Generally, a FIM is a standalone piece of information. This means if FIMs are used to indicate four different things, four different FIMs are required. Thus, the reader software must be programmed to look for each FIM independently. This results in increased reader execution time.
The width/height relationships of some FIMs make it difficult for simple methods of omni-directional detection. Simple scan based detection may fail when the FIM is rotated too far from the axis. In other words, it is not possible to draw a 45 degree line through the entire FIM.
FIMs also have the problem that they are not expandable/extendable in a manner that is transparent to the reading software. For example, if the USPS needed to expand from the four existing FIMs (A, B, C, D) to five, not only would the control programs which act on the FIMs need to be changed, but the underlying FIM reader software would need to be changed as well.
Finally, most FIMs were not designed for image based mail piece processing. While some image based processing equipment uses gray-scale imaging, other types of systems employ bi-level imaging (e.g., black and white) systems such as edge binarization imaging. As discussed above, depending on how these bi-level images are created, large black objects may be hollowed out. Reader software that has the functionality to cope with symbol hollowing is complex. Given the fact that FIMs are used only to convey their existence, the cost-benefit of this complexity is unappealing.
In another approach, linear one dimensional width modulated barcodes have been considered as a means to mark mail items. Some examples of linear bar codes includes interleaved 2 of 5, Code 128, and Code 39. Generally these type of codes are used to hold strings of data from a few characters to the low tens of characters.
Referring to FIGS. 3A–3C, diagrams of Code 128 symbols are shown. The Code 128 barcode shown in these Figures is the symbol for the character “A.” FIG. 3A is the gray scale imaging version of the symbol, FIG. 3B is a binarized version of the symbol, and FIG. 3C is the edge binarized version of the symbol. The more complex linear bar codes have some of the same issues described above. Again, the edge binarized symbol is shown as being hollowed out (third bar from the right). It is very difficult for the reader software to overcome this problem due to variable bar size and spacing which Code 128 allows. Barcodes are also subject to image based mail piece processing issues. As explained above, omni-directional detect/decode is an issue with bar codes as well. The narrow bars and spaces need to be wide enough for consistent reading at the resolution the image is being acquired at. Note that this generally causes the wide bars to be susceptible to bi-level hollowing.
Another drawback to using linear bar codes for mail processing relates to the fact that traditional linear width-modulated barcodes are overkill when only a small amount of information needs to be encoded. Most have Start and Stop Characters that may end up needing more space than the data being encoded.
To overcome the problems that the above examples illustrate, what is needed is a barcode that is simpler than traditional linear width modulated barcodes, but more complex than FIMs. In situations when only a small amount of information (perhaps 5 to 10 values) needs to be conveyed, neither FIMs nor existing linear barcodes are optimal. Thus, it is desirable to provide a bar code that can convey small amounts of information, and be edge binarization friendly. The new bar code must also be of a minimum size. It would also be beneficial if the new bar code were expandable, if necessary. The new bar code must be resistant to bar erosion/dilation causing no-reads/misreads. Finally the new bar code must be easy to detect/decode omni-directionally.